Brand: What kind of gas for 1967 Impala?

Article by: PAUL BRAND

March 29, 2013 - 1:06 PM

Q: I recently bought a one-owner ’67 Chevy Impala with only 73,000 miles that’s in very good shape. I’ve started a work list for spring that includes checking the antifreeze and transmission fluid and changing the fluids that need changing. The 327 V-8 engine is original and the owner left a note stating to add a lead additive if using a lower octane gasoline, but if non-oxygenated gas is used, no additive is needed. I filled it with non-oxygenated gas the day I picked it up in mid-December. Is it OK to start and run it every few weeks for the rest of winter?

A: First off, congratulations on finding a true “survivor” from the 1960s. Very few of these vintage vehicles are still original, unmolested and unrestored, which to my mind makes them even more appealing.

Let’s clear up some confusion here. Generally speaking, engines built before about 1970 required tetraethyl lead in the gasoline to provide two important requirements. First, lead was an inexpensive octane enhancer to increase the octane level of gasoline for higher compression engines. Second, lead provided a heat-transfer lubricating quality for valves. The lead helped transfer and dissipate heat from valve heads to valve seats to prevent burned valves. From about 1970 on, engines feature hardened valve seats and stellite or sodium-filled exhaust valves to handle more heat, negating the need for lead for this purpose. Today, tetraethyl lead is banned from road use motor fuels due to its toxic nature.

While the engine in your ’67 Impala was built for leaded gasoline, there’s likely more than enough lead buildup in this original engine to protect valve seats — particularly in light-load conditions like winter warm-ups and recreational driving. In fact, I wouldn’t worry about the engine when using today’s unleaded fuels unless you’re going to run the engine particularly hard. The correct choice of gasoline for your vehicle would be premium non-oxygenated to provide adequate octane as well as protect the fuel-system components from degradation due to the alcohol content of ethanol-blended gasoline.

But here’s the information you and the rest of us driving older vehicles need. Non-oxy gasoline is not a substitute for the lubricant quality of leaded gasoline. There are legal fuel additives classified as “metallics” that offer some of the heat-transfer capability of tetraethyl lead that you can use to protect valves and valve seats on older engines.

Since the only permanent “fix” for pre-1970s engines is to remove the cylinder heads to install hardened valve seats and new valves, I’d suggest driving the car until some type of symptom requires disassembling the engine. Upgrade the valves and valve seats at that point.

Q: My son owns a 2006 Mini Cooper. The muffler had a heat shield on it, which has fallen off. The Mini service center stated it was nothing to worry about. As a mother, I do worry about it. Should we be replacing the muffler?

A: On most vehicles, the heat shield on the exhaust system protects the catalytic converter, not the muffler. The reason is simple. Temperatures inside the converter can reach well over 1,000 degrees and the outside shell can reach 200 degrees or more. Mufflers typically don’t get that hot.

The heat shield protects the catalytic converter from coming into physical contact with — and potentially igniting — leaves, newspaper and other combustible materials. If the heat shield begins to rattle due to broken mounts, it can sometimes be reattached or secured by welding or steel straps. Once the shield is completely missing, the only fix is to replace the catalytic converter — a potentially expensive repair.

If the missing heat shield is part of or protects the muffler, I would be less concerned. The repair, which would involve replacing the rear half of the exhaust system, would be less costly.